The long-range objective of this project is to establish the function (or functions) of the pineal complex in vertebrates. To this end we have engaged in a comparative study that used rats, Japanese quail, and chickens. (Blood samples from humans have been tested in our bioassay for melatonin activity). We have extended our investigations to include an examination of the pineal complex in a number of species of lizards and related the results to their geographic distribution. This study revealed an apparent positive correlation between presence of the photoreceptive parietal eye (third eye) component of the pineal complex and distribution of the lizard to higher latitudes. We believe this supports the hypothesis, forwarded by others, that the pineal serves to synchronize reproduction with the appropriate season, as signalled by photoperiod. Continuing the comparative study of the pineal complex of vertebrates, we will direct our attention to the "lower" vertebrates with their more complex and remarkably varied pineal organs. Frogs and lizards will be the main subjects of the proposed investigations which seek to discover the possible role of the pineal in adaptations related to reproduction, homeostasis, thermal regulation, and protective coloration.